Raymond Hill, creator of uBlock Origin and uMatrix, reported the AdBlock Ultimate extension in 2017 but nothing came out of it. The AdBlock Ultimate extension has more users than Adguard currently Adguard has about 322k users, AdBlocker Ultimate 418K.
Rémi found mentions of AdGuard throughout the code of AdBlock Ultimate that suggest that code was copied from AdGuard.
The code of the extension is very similar to AdGuard, a very popular content blocking solution. Why is recommending an extension which seems to be a copy-pasting from another extension and potentially in copyright infringement? claims to be open-source and GPLv3 so I installed and checked the sources using the debugger. published the following message on Twitter today: One of the recommended extensions, AdBlocker Ultimate, appears to be a copycat extension. Other extensions are reviewed after the fact only, if at all. One of the main differences to regular extensions offered on Mozilla AMO is that recommended extensions are reviewed manually each time a new version is uploaded to Mozilla's site (and initially as well). that extensions need to be safe, but some are not. The new system accepts extensions only if they meet requirements some of these are self-explanatory, e.g.
The system used to select these changed recently from featuring extensions on Mozilla AMO to a stricter system.